Why does the board disconnect the USB connection?

I'm having a very hard time making a conenction to the board reliably.

I opened Arduino IDE, tried to upload:

ERR: Cannot find ameba on mbed driver! Please re-plug Ameba.

replugged, reuploaded, same thing:

ERR: Cannot find ameba on mbed driver! Please re-plug Ameba.

replugged, reuploaded again. Then it worked, BUT the serial monitor cannot be opened, because the board on COM3 is not available, which doesn't make much sense because I just flashed that board! Trying reupload:

ERR: Cannot find ameba on mbed driver! Please re-plug Ameba.

I replug and reuploaded several times more, then randomly being able to open the serial monitor, I see this printed:

Why does the board disconnect from USB? I have to replug the USB like 5 times before I can even upload a program, getting a serial monitor open isn't easy either. This is horrible. How can i keep the connection without replugging the USB all the time?

Once it works, it works kind of well and I can productively work with it: write code, flash, test, repeat, etc. It's the initila struggle of a random amount of replugging and recompiling that's annoying.